Clemens, in U.S. Pat. No. 3,842,194, has disclosed a system for recording and playback of information, including audio, video, and color information, capacitively. A high density information record has signal information in the form of a surface relief pattern in an information track, e.g., a spiral groove on the surface of the record. The record is made conductive with a metal layer, which acts as the first electrode of a capacitor, and then with a dielectric layer. The record is played back by means of a stylus electrode which is the second electrode of the capacitor. Since the record is rotated at a fairly high speed, on the order of 450 rpm, the friction between the stylus and the record surface may result in undue stylus wear. Thus a lubricant is applied to the surface of the record.
A suitable class of lubricants has been described by Matthies in U.S. Pat. No. 3,833,408, herein incorporated by reference. These lubricants have the general formula ##STR1## wherein R is an alkyl group of 4 to 20 carbon atoms and n is an integer.
Various improvements have been made to the record of Clemens including a record made from a conductive plastic which avoids the need for applying separate conductive metal and dielectric layers. Such a record may contain conductive particles for example. Improvement has also been made to the lubricant system. It has been found that when the lubricant is purified and fractionated, improved playback and storage stability results. The fractionated lubricant has the formula ##STR2## wherein R.sub.1 and R.sub.2 are alkyl groups of 4-20 carbon atoms, x is an integer of 2-4 and y is an integer of 0-2 and wherein the sum of x and y is 4 or less. These lubricants are described by Wang et al. in U.S. Pat. No. 4,275,101, also incorporated herein by reference.
Some problems still remain for the lubricated conductive record. The record surface has been found to be sensitive to moisture; that is, when the record is exposed to ambient conditions over a period of time, particularly including conditions of high relative humidity, a thin layer of organic and inorganic water soluble salt deposits form on the surface of the record, lifting the stylus during playback and interrupting the signal. This loss of signal has been termed "carrier distress". This carrier distress has been alleviated somewhat by careful cleaning and drying of the record surface which removes water soluble materials that have formed on the surface during molding operations. However, with time, additional water soluble materials and external debris form on the surface of the record, particularly in the presense of water vapor. Further, this requirement of cleaning and drying of the records adds to the cost of manufacture. It would be desirable to eliminate this extra processing of the disc.
Thus, more recently, the fractionated methyl alkyl siloxane lubricant has been doped with various materials including hydroxylated amines and polar silicones which have improved the resistance of the disc surface to carrier distress. We have insufficient knowledge at the present time about the nature of the disc surface to predict which materials will be effective in reducing susceptability of the disc to degeneration of playback after exposure to heat and high relative humidity.
Up until now, hydrocarbon lubricants have been ineffective to lubricate the disc surface, even though as a class hydrocarbon lubricants have improved resistance to oxidation, moisture, and shear stress. We believe that this is due to the fact that the disc surface is highly polar, whereas hydrocarbons are non-polar and thus the problem is they do not wet the surface of the disc well or adhere well to the disc surface, particularly after playback.